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HUAWEI EM820W HSPA+ PC Embedded Module
Hardware Guide RF Specifications
Issue 01 (2010-12-31)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
20
4.4 Antenna Design Requirements
4.4.1 Antenna Design Indicators
Antenna Efficiency
Antenna efficiency is the ratio of the input power to the radiated or received power of
an antenna. The radiated power of an antenna is always lower than the input power
due to the following losses: return loss, material loss, and coupling loss. The
efficiency of an antenna relates to its electrical dimensions. To be specific, the
antenna efficiency increases with the electrical dimensions. In addition, the
transmission cable from the antenna port of the EM820W to the antenna is also part
of the antenna. The cable loss increases with the cable length and the frequency. It is
recommended that the cable loss should be as low as possible, for example, U.FL-
LP-088 made by HRS.
The following antenna efficiency (free space) is recommended for the EM820W on a
laptop to ensure high radio performance of the EM820W:
z
Efficiency of the master antenna > 40% (-4 dB)
z
Efficiency of the slave antenna > 40% (-4 dB)
z
Efficiency of the GPS antenna > 50% (-3 dB)
z
Efficiency of the Wi-Fi antenna > 40% (-4 dB)
Isolation
For a wireless device with multiple antennas, the power of different antennas is
coupled with each other. Antenna isolation is used to measure the power coupling.
The power radiated by an antenna might be received by an adjacent antenna, which
decreases the antenna radiation efficiency and affects the running of other devices.
To avoid this problem, evaluate the antenna isolation as sufficiently as possible at the
early stage of antenna design.
Antenna isolation depends on the following factors:
z
Distance between antennas
z
Antenna type
z
Antenna direction
The master antenna must be placed as near as possible to the EM820W to minimize
the cable length.
The slave antenna needs to be installed perpendicularly to the
master antenna. The slave antenna can be placed farther away from the EM820W.
Antenna isolation can be measured with a two-port vector network analyzer.
The following antenna isolation is recommended for the antennas on laptops:
z
Isolation between master and slave antennas < -12 dB
z
Isolation between the master antenna and the GPS antenna < -15 dB
z
Isolation between the slave antenna and the Wi-Fi antenna < -15 dB
If a Wi-Fi module is installed on the laptop, the following measures must be taken to
reduce mutual influence between the data card module and the Wi-Fi module: